In a free-space line-of-sight link, which equation correctly yields the received power Pr in dB given Pt, Gt, Gr, and Lp?

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Master the AN/PRC-160 and AN/PRC-163 Radio Operations Test. Utilize flashcards and multiple choice questions, each with hints and explanations. Ace your exam!

Multiple Choice

In a free-space line-of-sight link, which equation correctly yields the received power Pr in dB given Pt, Gt, Gr, and Lp?

Explanation:
The main idea is that, in a free-space line-of-sight link, the received power in decibels is found by taking the transmitted power in decibels, adding the antenna gains (also in decibels) for both the transmitter and receiver, and then subtracting the path loss (in decibels) that the signal experiences as it travels. Gains boost the power, while the path loss reduces it, so the signs must reflect that: Pr_dB = Pt_dB + Gt_dB + Gr_dB − Lp_dB. This is the decibel form of the Friis transmission relation. If you see a form that subtracts the antenna gains or adds the path loss, those don’t match the physical effect of each term on the received power. In linear terms, the relationship is different, but in dB, gains add and losses subtract.

The main idea is that, in a free-space line-of-sight link, the received power in decibels is found by taking the transmitted power in decibels, adding the antenna gains (also in decibels) for both the transmitter and receiver, and then subtracting the path loss (in decibels) that the signal experiences as it travels. Gains boost the power, while the path loss reduces it, so the signs must reflect that: Pr_dB = Pt_dB + Gt_dB + Gr_dB − Lp_dB. This is the decibel form of the Friis transmission relation.

If you see a form that subtracts the antenna gains or adds the path loss, those don’t match the physical effect of each term on the received power. In linear terms, the relationship is different, but in dB, gains add and losses subtract.

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